Conventionally, for this type of flow rate measuring system, systems have been used wherein the amount of fluid filled into the individual containers into which fluid is filled is monitored using an electromagnetic flow meter.
Because it is necessary to fill the fluid continuously into a plurality of containers, in this system the individual filling tubes for filling the fluid into the containers, and the individual electromagnetic flow meters that are provided for each individual filling tube, are disposed in proximity to each other. In particular, the degree of intimate contact between the individual flow tubes becomes high when the containers are small.
In this system, the flow rate of a fluid that flow rates in each filling tube is measured by an individual electromagnetic flow meter based on an electromotive force (an electromotive force that is generated between signal electrodes) that is generated through the application of an alternating magnetic field to the fluid within each individual filling tube. In this case, when the degree of intimate contact between the individual filling tubes is high, the differential noise that is generated at the time of switching of the square-wave excitation magnetic field (that is, at the time of switching the alternating field) will have a mutual effect on the adjacent electromagnetic flow meters as leaked magnetic flux from the magnetic excitation coils.
In the electromagnetic flow meter, the magnetic excitation timing is determined based on individual clock signals. Because of this, there will be some small variability in the magnetic excitation frequency in the individual electromagnetic flow meters. In such a case, even if initially the magnetic excitation timing matches between the individual electromagnetic flow meters, mismatch will appear in the magnetic excitation timings as time elapses. Given this, if there is a switch in the square wave magnetic field in an adjacent electromagnetic flow meter during the sampling interval of the electromotive force that occurs between the signal electrodes, then error will be included in the value measured for the flow obtained from the electromotive force. That is, a spike will occur in the alternating current flow speed signal due to the influence of the differential noise from the adjacent electromagnetic flow meter and this spike will be sampled. Because of this, the fluid fill volumes will vary between the plurality of containers, and repeatability will be poor for the fill volume.
Given this, in, Japanese Unexamined Patent Application Publication 2001-348092 (“JP '092”) one of the electromagnetic flow meters, which are provided for each individual filling tube, is defined as a master flow meter, and the other electromagnetic flow meters are defined as slave electromagnetic flow meters, where the master electromagnetic flow meter and the slave electromagnetic flow meters are connected in series with a synchronization signal line, where the synchronization signal that is produced in the master electromagnetic flow meter is sent to all of the slave electromagnetic flow meters as a master synchronization signal.
In the system illustrated in JP '092, the master electromagnetic flow meter performs flow rate measurement by generating the magnetic field with the magnetic excitation timing synchronized to a synchronization signal that is generated within its own synchronization signal generating unit. The slave electromagnetic flow meters perform flow rate measurements by producing a magnetic fields with magnetic excitation timings that are synchronized to a synchronization signal that is sent, either directly or indirectly, from the master electromagnetic flow meter (that is, synchronized to a master synchronization signal). As a result, the flow rate measurements are performed by all of the electromagnetic flow meters generating the magnetic fields with identical magnetic excitation timings.    Japanese Unexamined Patent Application Publication 2001-348092
However, in the system illustrated in JP '092, if the master electromagnetic flow meter were to have a fault, if there were a fault in the synchronization signal line between the master electromagnetic flow meter and the slave electromagnetic flow meters, if there were a fault in a synchronization signal line between slave electromagnetic flow meters, if there were a fault in the circuit for receiving the synchronization signal in a slave electromagnetic flow meter, or if there were faulty communications such as noise on the synchronization signal lines, then this would produce a state wherein or more slave electromagnetic flow meters are incapable of receiving the master synchronization signal from the master electromagnetic flow meter. In this case, any slave electromagnetic flow meter that cannot receive the master synchronization signal would not be capable of performing the flow rate measurement, and thus the operation of filling the fluid into the container from the filling tube in which the slave electromagnetic flow meter is provided would be interrupted, reducing productivity.
The present invention was created in order to solve this type of problem, and the object thereof is to provide a flow rate measuring system capable of continuing flow rate measurements in a slave electromagnetic flow meter, even when there is an interruption in the synchronization signal from the master electromagnetic flow meter (that is, an interruption in the master synchronization signal) due to communication faults, or the like.